scons: minor cleanup
scons: minor cleanup

(cherry picked from commit 745e393fd694908977d9ab5a38ded3446fed88b3)

lightmare/mapnik,lightmare/mapnik,naturalatlas/mapnik,lightmare/mapnik,naturalatlas/mapnik,naturalatlas/mapnik,tomhughes/mapnik,lightmare/mapnik,tomhughes/mapnik,mapnik/mapnik,tomhughes/mapnik,mapnik/mapnik,tomhughes/mapnik,mapnik/mapnik,naturalatlas/mapnik,mapnik/mapnik